1. Field of the Invention
The invention generally relates to an inorganic fluorescent material used for a solid-state light source, and more particularly to an inorganic fluorescent material containing a phosphor that generates a yellow fluorescent light after being excited by a blue solid-state light source so as to generate a white mixed light.
2. Description of the Related Art
Recently, the process of producing a solid-state light source has been continuously developed with increasingly higher illumination efficiency. Since it emits a light wavelength close to monochromic light and has many advantages such as high reliability, long service life and a wide range of application, the solid-state light source has increasingly replaced the traditional vacuum bulb in illumination equipment.
In the prior art, generating white light by means of the solid-state light source includes two methods. One of them mixes red, green and blue lights respectively emitted from their light source to generate white light. This method is called a RGB method. In this method, the mixed light color is not uniform due to cell orientation in the solid-state light source. Furthermore, the illumination intensity is not completely utilized. In the second method, a phosphor layer is applied on the blue solid-state light source, the phosphor layer emitting yellow fluorescent light after being excited by blue light for obtaining white light of a color temperature of about 8000K. U.S. Pat. No. 5,998,925 (“the '925 patent”) discloses a light emitting device consisting of a nitride semiconductor and a phosphor containing a garnet fluorescent material, which operates according to the second method. In the '925 patent, a solid-state light source chip is mounted in a casing with a recess or an inwardly bent portion therein, and then a resin coat containing the phosphor fills up the recess or the inwardly bent portion of the casing. The material for a solid-state light source chip includes IniGajAlkN (i+j+k=1) nitride. The phosphor includes (a) at least one element selected from YLuSeLaGd and Sm, and (b) at lease one element selected from AlGa and In; the phosphor is activated by Ce. More specifically, the phosphor includes the general formula of (Y1-p-q-r, GdpCeqSmr)3(All-sGas)5O12, wherein 1□p □ 0.8, 0.003 □q□ 0.2, 0.0003 □r□0.08, and 0□s □ 1, to obtain the light of required wavelength with improved luminance efficiency.